This application claims the priority benefit of Taiwan application Ser. No. 90111229, filed May 11, 2001.
1. Field of Invention
The present invention relates to a method for reducing roughness of the photoresist. More particularly, the present invention relates to a method for reducing roughness of the photoresist through cross-linking reaction of deposit and the photoresist.
2. Description of Related Art
The technique of the photolithography is a very important step in the manufacture process of the semiconductor device. Almost every element in the structure of the MOS device, for example, the pattern of each layer or the doping region, relates to the step of photolithography. As the integration becomes higher, the size of the device keeps decreasing, for a smaller line-width. However, it is also decided by the technique of photolithography whether the line-width can be smaller.
The conventional photolithography process steps include coating, pre-exposure bake (i.e. soft bake), exposure, post-exposure bake, development and hard bake. In the development step, the developer is used to remove undesired photoresist layer, so that the transferred pattern is shown. As shown in FIG. 1, a photoresist pattern 102 is formed over a substrate 100. However, the surface of the line edge of the photoresist pattern 102 is pretty rough, further deteriorating accuracy of the pattern, uniformity of the critical dimension, the yield and the process window. Therefore, it is desired to reduce roughness of the photoresist for ensuring accuracy of the following processes.
The conventional methods for reducing line edge roughness (LER) are raising the temperatures for the soft bake process and the post-exposure bake process, so that the amount of solvent in the photoresist is reduced, thus improving LER of the photoresist pattern. However, it is limited by the structure of the photoresist. Usually, the temperatures for the soft bake process and the post-exposure bake process are maintained between 90 to 110xc2x0 C. If the temperatures are raised to too high, roughness or wrinkles are formed in the surface of the photoresist, failing to improve LER of the photoresist pattern.
The invention provides a method for reducing roughness of the photoresist through cross-linking reaction of deposit and the photoresist. A material capable of cross-linking with the photoresist is deposited over the photoresist pattern, to reduce line edge roughness of the photoresist pattern.
The invention provides a method for reducing roughness of the photoresist through cross-linking reaction of deposit and the photoresist. By increasing the concentration of hydrogen ions on the surface of the photoresist pattern, the effect of cross-linking between the deposit and the photoresist is enhanced, thus reducing LER of the pattern. Therefore, uniformity of the critical dimension (CD), the yield and the process window are increased.
The invention provides a method for reducing roughness of the photoresist through cross-linking reaction of deposit and the photoresist. The method comprises at least performing an exposure process to a substrate having a photoresist pattern and performing a post-exposure bake process for activating the surface of photoresist pattern. A material layer is formed to cover the surface of the photoresist pattern. The material layer cross-links with the hydrogen ions on the surface of the photoresist pattern, so that a filling layer is formed to fills asperity or the rough regions of the photoresist pattern.
One of the features of the present invention is to deposit a material that can cross-links with the hydrogen ions on the surface of the photoresist pattern over the developed photoresist pattern. Therefore, the rougher the surface of the photoresist is, the more contact regions there are for the cross-linking reaction between the photoresist and the deposited material. As a result, more reaction products are formed to fill and improve LER of the photoresist pattern.
Furthermore, the developed photoresist pattern has higher hydrogen ion concentration, which helps speed up the cross-linking reaction and increase the amount of reaction products.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.